Solar System NotesMeasuring Up!Science Lesson 24

Galaxies

California Standards8.4.a: Students know galaxies are clusters of billions of stars and may have different shapes.8.4.c: Students know how to use astronomical units and light years as measures of distances between the Sun, stars, and Earth.

Language of the DisciplineA galaxy is a cluster of billions of stars

and associated gas and dust in space that is bound by gravity.

A nebula is a large cloud of dust and gas where stars are born in space.

A light year is a unit of length equal to about 9.5 trillion kilometers. It is the distance that light can travel in one year.

An astronomical unit (AU) is the unit of length equal to the average distance from the Sun to the Earth.

Measuring Up!Guided InstructionRead page 161 to the top of page 162 in the MU book.

Guided QuestionsHow is the universe currently

changing?The universe is expanding.

What are galaxies made up of?Groups of billions of stars and solar systems.

Measuring Up! Guided InstructionRead the chart on page 162 in the MU book.

Galaxy Type Description Illustration

Spiral galaxy curved bulge in the center that is surrounded by revolving spiral arms

Milky Way (our galaxy)

Elliptical galaxy massive blobs of stars that are spherical or ovular in shape

oldest stars

Irregular and dwarf galaxies

Irregular: do not belong to spiral or elliptical, no definite shape

Dwarf: small

Guided QuestionsWhat kind of stars are often found in

elliptical galaxies?The oldest stars.

Measuring Up! Guided InstructionRead the rest of page 162 in the MU book.

Guided QuestionsWhat is a light year?The distance light travels in one year.

More Guided QuestionsList four kinds of galaxies.spiral, elliptical, irregular, dwarfHow many astronomical units away

are we from the Sun?1 AUApproximately how many kilometers

are in 2 light years?19 trillion kilometers

Independent Practice:① Read page 163

in the MU book.② Complete the

Apply questions in your packet.

③ Complete the Assessment Practice in your packet.